Semiconductor chips or integrated circuits (“ICs”) used in semiconductor devices are initially fabricated on wafers. After fabrication the wafers are then cut to separate the semiconductor chips, after which the semiconductor chips are usually assembled into packages to protect them from mechanical stress. In general, the package assembly process includes mounting a plurality of the semiconductor chips from the wafer onto a carrier such as a leadframe, forming wire bonds between the semiconductor chips and the leadframe and then encapsulating the semiconductor chips with a molding compound. Following molding, the leadframe with encapsulated semiconductor chips is trimmed, formed and the semiconductor chips are separated into individual packaged semiconductor devices. This is commonly referred to as a singulated semiconductor device.
After packaging, the semiconductor devices have to be electrically tested to make sure they are free of any manufacturing defects. Presently, packaged semiconductor devices may be electrically tested after a trim process, as the devices are electrically isolated after trimming, but retain their relative positions on the carrier. This method of testing allows a plurality of semiconductor devices to be contacted and tested at the same time so as to improve testing efficiency. Alternatively and more commonly, semiconductor devices may be tested when they are in singulated form. However, even in singulated form, semiconductor devices may be arranged in a matrix or array format onto a carrier device and then presented to a tester. This method also facilitates a plurality of semiconductor devices to be contacted and tested at the same time.
In these two methods of testing, the test interface typically employed between the tester and the semiconductor devices under test consists of densely populated spring-loaded contact probes housed within an mounting block. The spring-loaded contact probes provide an electrical interface between the tester resources and the electrical contacts or leads of the devices under test. A standard spring loaded contact probe typically consists of a barrel, an internal spring and a moveable plunger at each end of the barrel. The plunger tip at one end of the barrel is to make contact with an interface board of the tester device (“Device Interface Board”) while the plunger tip at the other end of the barrel is used to contact the electrical leads of the devices under test. The plunger tip when in contact with the device is compressed further by a certain travel distance to provide the required spring force to penetrate oxides on the lead to thereby ensure reliable contact.
While the spring-loaded contact probe can cater to quite a number of testing applications, the current carrying capacity of the spring-loaded probe is mostly inadequate for testing high power devices. It was found that when a very high pulse current (for example, 200 Amperes at 1 millisecond pulse rate) is injected through a spring loaded contact probe, hot spot regions are found at the plunger, barrel and spring interfaces. Common problems encountered include melting at the interfaces and spring collapse with stuck pins being a common occurrence. It would be desirable to introduce a one-piece contact probe design for minimizing a risk of failure of the probe at its interfaces.
U.S. Pat. No. 5,667,410 for a “One-Piece Compliant Probe” discloses a contact probe for an electronic tester in which the probe includes a one-piece contact probe having a plunger member and a compliant spring section contained in and guided for spring biased axial travel in a tubular outer barrel. The plunger member, spring section and barrel are jointly formed of a single integral spring metal piece. The purpose of this invention is to provide a solid metal compliant electrical connector for carrying high loads subjected to constant cycling. However, a drawback of such a contact probe is that it is made from sheet material, thereby occupying a relatively larger area as a whole when assembled. Another disadvantage is that it has only one plunger member. It would thus not be as flexible as a double-ended contact probe which can contact both the device under test on one end and the Device Interface Board connected to testing resources on the other end. In addition, by housing the spring metal piece within a barrel, the sliding contact between plunger/spring and barrel under very high current pulses will still cause hot spot regions and melting at the interface like conventional spring probes. This may dramatically reduce the lifetime of the probe.